Receiving circuit



J. B. Moons RECEIVING CIRCUIT Filed Nov; 25, 1953 Sept 2 s eetg V1 f/Z72-77 (194w em) N P- am.

INVENT I JOHN MOORE BY TORNEY 70 5/4: W F A/m/nm;

p 1937. J. B. MOORE RECEIVING CIRCUIT Filed Nov. 23, 1955 2 Sheets-Sheet2 0 0 M 5 4 w W K C OFF M/D BAND INVENTOR JOHN B'.MOOHE BY d JWM/ATTORNEY Patented Sept. 14, 1937 UNITED STATES 2,092,890 RECEIVINGomoorr John B. Moore, Riverhead, N.

Y., assignor to Radio Corporation of America, a corporation of DelawareApplication November 23, 1933, Serial No. 699,318

8 Claims.

This .invention relates to multiple detection radio receiving circuitsand is particularly concerned with the intermediate frequency stages ofsuch receivers.

Due to the fact that radio receivers now in general use have a fixedfrequency band width, it is necessary in the reception of various typesof service to have as many different types of receivers as there aredifferent services. As an illustration, in the reception of telephone,program or facsimile service it has been found that a receiver having arather wide frequency band width is required, whereas, at other times,in order to receive telegraph signals and to prevent inter ference fromadjacent channels it is necessary to have a much narrower frequency bandwidth. In the use of short waves particularly, where varying channelspacings are involved, it isusual to have a plurality of receivers tohandle the different types of services.

Heretofore in the use of these receivers, particularly those of themultiple detection type, the construction of the apparatus has not beensuch as to lend itself readily for use with different services,especially so since there is required in this type of apparatus a changeof the band width in the intermediate frequency amplifier system foreach type of service. To accomplish such a change has involved in mostcases retuning of the coupled circuits, a change which is ratherdifficult for inexperienced operators who have a limited knowledge ofthe radio art. It has further been found that if several circuits areused, the process of changing over from one band width to another inorder to obtain a desired selectivity is rather a slow and tediousproposition even for an experienced operator.

It is an object of the present invention to overcome these disadvantagesby providing greater flexibility in radio receiving systems so as toenable quick and efiicient change-over in a receiver from one band widthto another.

Another object is to provide such a change-over system wherein theswitching from one band ,width to another is done in a quick andefiicient manner and by the use of simple switching mechanism.

Briefly, the present invention contemplates the use in a multipledetection receiver of an interchangeable filter arrangement comprising aplurality of filter units in the second intermediate frequencyamplification stage for obtaining instant change-over of the band widthin the receiver. To accomplish this, there is employed simple switchingmechanism for switching from one filter unit to another. Thus, thereisobtained an arrangement which permits instant changing over to be madein a very simple way by even the most inexperienced operators.

One advantage of the present invention has 5 been'found to reside in thefar greater degree of selectivity which can be obtained than from anequal number of transformer coupled stages of amplification.

In the accompanying drawings, Figure 1 shows, diagrammatically, amultiple detection receiver embodying the features of the presentinvention, and Figure 2 illustrates, graphically, the band widthsavailable from the receiving system depicted. i 15 Referring to Figure 1in more detail, there is shown .a well known type of triple detectionreceiver comprising a plurality of radio frequency stages I and 2coupled to a detector 3 which, in turn, is arranged to produce, incombination with an oscillator 4, a beat frequency which is supplied tothe first intermediate frequency amplifier' stage 5. A filter unit 22 inthe output of amplifier stage 5 serves to provide part of the desireddegree of selectivity required. From this filter unit, the signals atthe beat frequency are fed to intermediate frequency detector 1 wherethey combine with oscillations from an intermediate frequency oscillator6 which serves to produce ,in they output of detector 1 a lowerfrequency beat note which is fed to the first stage 8 of the secondintermediate frequency circuit and ,then through a desired intermediatefrequency filter-unit of :the interchangeable filter arrangement andother stages of the second intermediate :35 frequency amplifier to thefinal detector 9 ,from which the audio frequency components are passed to any suitable utilization circuit It].

In the particular embodiment shown, the tuning-is accomplished intheradio'frequency amplifier stages I and 2, the tunings of theindividual intermediate frequency filters H and I2 of theinterchangeable filter arrangement being fixed in their design once andfor all. These interchangeable filters have any suitableband widthsand:. 4 5 are provided-With a single pole,v double throw switch at theinput and output ends of the filter for enabling proper switching of theamplifier from one filter to the other. As indicated in the drawings,the operation of the switch by means of a unicontrol arrangement hereindesigned by the dotted line 2| connects the anode lead M of the inputtube 8 in the second intermediatefrequency amplifier to either one ofthe filters and also switches simultaneously the control grid I5 of thefollowing tube l9 to the corresponding filter. These filters may be anyof the well known types which may be used to determine the overall bandwidth of the receiving equipment, and since 5 the design of the filter,per se, forms no part of the present invention it will not be describedherein.

By the use of switching mechanism l3 one is easily enabled to quicklychange the band width of the receiver merely by interchanging the filterunits and thus to provide a quicker and more advantageous scheme thanthat obtained by the use of tuned transformers between the stages.

Figure 2 illustrates, by way of example only, 15 suitable different bandwidths which may be ob-' tained by means of the present invention.In'this' figure, graph A represents a band width of twenty kilocycleswhich is the band width passed by the first intermediate frequencyfilter, andgraph B illustrates a band width of ten kilocycles which oneof the filters I2 is designed to pass, let us say, for program service.Graph C, however, shows a three kilocycle band width which filter ll,may be designed to pass, for another type of service.

The present invention, it is to be understood, is not limited totheprecise arrangements shown since numerous modifications may be madeby those skilled in the art without departing from the spirit and scopeof the invention. For ex ample, instead of the two filter circuitsshown, any two channels having different band width characteristics maybe employed.

I claim:

l. The combination in a multiple detection receiving circuit having ahigh frequency amplification system and at least one intermediatefrequency amplification system operatively connected thereto, of aninterchangeable filter arrangement selectively'connectable in circuitwith 40 said intermediate frequency amplification system,

said filter arrangement comprising a plurality of filters havingdifferent frequency ranges mutually inclusive of a given mid-bandfrequency and switching mechanism for operatively associating 45 saidintermediate amplification system with any one of said filters.

2. A super-heterodyne receiving circuit comprising a radio frequencyamplification system, a first intermediate frequency amplificationsystem 5 including a band-pass filter, and a second intermediatefrequency amplification system, said last system comprising a firstelectron discharge tube having an output circuit and a second electrondischarge tube having an input circuit, a plurality of filters havingsubstantially identical mid-band frequency characteristics but differingone from another as do their respective frequency ranges, said filtersbeing interposed between the output of said first tube and the input ofsaid 60 second tube, and switching mechanism in said output and inputcircuits for connecting said input and output circuits with one of saidfilters at a time.

3. A receiver as defined in claim 2 characterized 5 in this, that saidswitching mechanism comprises two unicontrol single pole double-throwswitches.

4. In combination, an electron discharge device having an input circuitand another electron discharge device having an output circuit, twobandpass filter units between said input and output circuits, one ofsaid band-pass units having a pass range substantially centrallydisposed within the pass range of said other filter unit, and means forselectively connecting one only of said band-pass unit's simultaneouslyto said input and output circuitsf g 5. A super-heterodyne receivingcircuit comprising a radio frequency amplification system, a firstintermediate frequency amplification system including a band-pass filterhaving a band-pass range of at least 20 kilocycles, and a secondintermediate frequency amplification system, said last system comprisinga first electron discharge tube having an output circuit and a secondelectron discharge tube having an input circuit, a plurality ofband-pass filters between the output of said first tube and the input ofsaid second tube, one of said filters having a band-pass range of atleast kilocycles and 'the other of said filters having a band-pass rangeof at least 3 kilocycles within said 10 kilocycle range, and switchingmechanism in said output and input circuits for connecting said inputand output circuits with one of said filters at a time.

6. In a super-heterodyne receiving circuit, an intermediate frequencyamplifying system comprising an electron discharge device having aninput circuit and another electron discharge device having an outputcircuit, two band-pass filter units between said input and outputcircuits, said units having the same mid-band frequency but differentband widths, and switching mechanism in said input and output circuitsfor operatively connecting said electron discharge devicessimultaneously with one of said two filter units, but not with both.

7. In a superheterodyne receiving circuit, a.

radio frequency amplification system, a first intermediate frequencyamplification network connected to said system and including a bandpassfilter, and a second intermediate frequency amplification networkadapted to be fed with energy from said filter, the last said networkhaving interposed between two of its stages a plurality of selectivelyconnectable band-pass filters each of progressively more and morerestricted frequency range than the range of the first said band-passfilter, and each having substantially the same mid-band frequency asthat of the others.

8. In a receiving system, an" energy collecting circuit, an outputcircuit, a pair of filters each having different pass widths but adaptedto pass the same mean frequency, and switching means associated withsaid energy collecting circuit and said output circuit for selectivelycausing the transfer of energy from said energy collecting circuit tosaid output circuit through either one only of said filters during anyparticular period of time.

- JOHN B. MOORE.

